1. Field of the Invention
The present invention relates to a solenoid valve for a brake system, and more particularly, to a solenoid valve for a brake system capable of being more easily manufactured and reducing manufacturing costs.
2. Description of the Related Art
Generally, an anti-lock brake system for vehicles serves to prevent locking of wheels by sensing slippage of the wheels and suitably controlling braking pressure applied to the wheels. The wheels of the vehicle do not slip during braking by means of the anti-lock brake system, whereby the steering performance of the vehicle is maintained, and the vehicle is stopped safely.
In order to control braking pressure, the brake system includes a plurality of solenoid valves to open or close a fluid path of a braking hydraulic pressure line. The solenoid valves include normal open type solenoid valves which are normally kept in an opened state, and normal close type solenoid valves which are normally kept in a closed state.
FIG. 1 shows a conventional normal open type solenoid valve. A conventional normal open type solenoid valve includes a valve core 1 which is formed with a through-hole 2 at a center thereof in a longitudinal direction and an outlet 3 in a radial direction, a dome-shaped sleeve 4 which is mounted to an upper portion of the valve core 1 to cover the same, an armature 5 which is slidably mounted in the sleeve 4, and an exciting coil 6 which is mounted around the sleeve 4 to slide the armature 5.
Inside the through-hole 2 of the valve core 1 are mounted a plunger 7 which slides by the movement of the armature 5, a valve seat 8 having an orifice 8a which is opened or closed by the plunger 7, and a restoring spring 9 which presses the plunger 7 toward the armature 5 to open the orifice 8a when electric power is not applied to the exciting coil 6.
When electric power is applied to the exciting coil 6, the armature 5 moves toward the valve core 1 by a magnetic force exerted between the armature 5 and the valve core 1. The plunger 7 moving toward the valve seat 8 closes the orifice 8a. When electric power is not applied to the exciting coil 6, the magnetic force is removed, and the plunger 7 moves away from the valve seat 8 by an elastic force of the restoring spring 9, thereby opening the orifice 8a. By the orifice 8a being repeatedly closed and opened by the movement of the plunger 7, the solenoid valve intermits oil supply flowing through the braking hydraulic pressure line.
When the braking operation is performed, oil flows into the solenoid valve through an inlet passage formed in a lower portion of the valve core 1, and then flows toward the outlet 3 formed at a side portion of the valve core 1 via the orifice 8a. When the braking operation is released, the oil flows through a gap between an outer lower surface of the valve core 1 and an inner surface of a bore 12 of a modulator block 11, as shown by an arrow A in FIG. 1, so that the oil can rapidly return. To achieve this, a lip-seal 13 is mounted on the outer lower surface of the valve core 1, which permits the oil flow only in the return direction.
However, the above-described conventional solenoid valve has a shortcoming of difficulty in manufacture due to a complicated shape of the valve core. That is, when manufacturing the valve core, a plurality of stair-shaped stepped portions should be formed on the outer surface of the valve core through a cutting process, and also the through-hole and the outlet should be formed in the valve core through a cutting process. This causes problems of difficulty in manufacture and high manufacturing costs.
Further, because the sleeve is coupled to the valve core through a welding process, the above-described conventional solenoid valve also has shortcomings of high work effort and low assembling productivity.